Widespread microcystins accumulation in fish of several trophic guilds in reservoirs of a dry area in Central México

The effects on human health from exposure to cyanotoxins during cyanobacterial blooms have been reported worldwide. Accumulation of toxins in fish has been documented as a potential route of transfer to humans through the ingestion of contaminated food. In this study, we determined the magnitude of microcystin (MCYSTs) concentrations in six reservoirs in central Mexico to assess the potential risk of toxin transfer to humans through the consumption of fish. Physicochemical parameters, phytoplankton composition, and MCYSTs concentrations were analyzed in water, seston, and tissue of nine fish species with varying trophic habits. We detected MCYSTs in all reservoirs, both dissolved and in seston, with the highest concentrations recorded in the Batán and Carmen reservoirs, where Microcystis was the dominant cyanobacterial genus. All fish species showed accumulation of MCYSTs, with Goodea atripinnis (phytoplanktivore) and Chirostoma jordani (zooplanktivore) exhibiting the highest concentrations in viscera and whole-body analyses. The estimated daily intake derived from consuming 100 g of contaminated fish frequently exceeded the WHO tolerable daily intake of 0.04 μg/kg body weight, indicating potential risks to human health. This finding evidences a widespread presence of hepatotoxic MCYSTs in reservoirs of central Mexico in water (regardless of the occurrence of visible blooms), seston, and accumulated in tissues of fish species. This study represents the first report of MCYSTs accumulation in fish tissue from different trophic habitats in reservoirs in central Mexico and emphasizes the need for ongoing cyanotoxin monitoring and management measures to mitigate risks to both aquatic ecosystems and human consumers.